textproduct: Quad Cities

KEY MESSAGES

- Because of the heavy rain this morning in many places and the chance for more storms, A flash flooding threat will continue south of Hwy 30 into the evening.

- Quiet and somewhat cooler than normal weather will be seen through the second half of the work week, with the pattern becoming active again this weekend and beyond.

UPDATE

Issued at 1135 AM CDT Wed Jun 17 2026

Our focus is now on the assessment of morning storms and their effect on the afternoon activity. While there is a notable imprint on the temperature field, one challenge with this event is that it is far more spring-like than summertime. In other words, the strength of the low pressure (992 mb) will help drive parameter fields by stronger advection than we would typically see in June. As a testament to this is an impressive June temperature gradient across the area with mid to upper 50s north and central to low 80s just south of the CWA.

The surface warm front modulated by outflow from the morning storms is draped just south of the CWA border. Strong WAA aloft and moisture transport are resulting in regularly developing thunderstorms near the 850 mb frontal zone over the I-80 corridor, with mainly a flash flood threat. Also impressive cloud-to-ground lightning even when rain rates diminish some. Near the surface warm front, satellite indicates fairly solid cloud cover near the Iowa/Missouri border. However, some of this is transitioning to towering cumuliform clouds from near Ottumwa southwestward along a confluence axis. We are thinking this may be the start of the afternoon round of storms as it progresses eastward across locations near/south of U.S. Highway 34, and likely some gradual northeast expansion, possibly even near to the I-80 corridor in Illinois.

As upper forcing from a 120 kt upper jet impinges over this area, mature convection should gradually develop. These storms will be at least close to being rooted in the boundary layer, but even if slightly elevated will have severe potential. The parameter space remains favorable for significant severe weather, including hail even though we did not have much with the morning activity. Of greater concern is if rooted in the boundary layer there would be the threat of tornadoes, some potentially significant given a stout parameter gradient (as shown by a forecast STP gradient of 1-6 by 3 PM). Whether that truly manifests into surface-based supercells in our CWA is still an uncertainty.

Now this is not to say there is not a severe, and even a lower end tornado threat, further north toward Iowa City and the Quad Cities, simply because of the dynamics with this system. Dew points in the mid 60s have returned to central Iowa on southeast winds, and continued pressure falls will help keep that low-level theat-a advection increasing ahead of the low pressure. In tandem with effective shear in the 1-6 km layer of 50+ kts, at least some organization for scattered severe is plausible, and we'll have to keep a close eye on the low-levels. As long as storms keep regenerating along this I-80 corridor, it may prevent true low-level warming and CAPE from building up to the I-80 corridor in our CWA.

Confidence is high in any severe weather threat clearing our area near 7 PM. Isolated showers and storms in northwest Illinois may continue to 9 PM before the forcing has pushed east.

SHORT TERM /THROUGH THURSDAY NIGHT/

Issued at 225 PM CDT Wed Jun 17 2026

Building upon the Update discussion above, increasing shear profiles with the arrival of stronger wind flow at several levels is occurring, with effective shear profiles of 50-60 KTs. A secondary warm front lifting up to the I-80 corridor while a cool front is squeezing eastward acrs western into central IA. But the prime interaction with building/re-building instability/CAPEs with a sharp tight gradient is aligning along an agitated CU field seen on the VIS satellite loop from acrs west central ILwest-southwestwrad acrs far northern MO and west of the Kansas City area. This is where new supercellular storm development is expected soon, thus the DVN southern third to quarter of the CWA will be at risk for this development, with the activity then slipping south of the CWA through late afternoon. The other action zone of mainly elevated storms closer to the upper low/trough will rotate acrs southern MN, far northeast IA and into WI through mid evening, possibly making the bulk of the DVN CWA in between these two main convection zones. Thus there may be just a few stray elevated showers or storms moving acrs the local area after the potential storms in our south migrate southward to CAPE feed, but may still have to watch the strength of these "in-between" storms.

Post frontal west-northwesterly boundary layer feed to bring about low temps down in the 50s for much of the area by Thursday morning. Later on Thursday looks like a blustery post-frontal day with plenty of cumulus development and/or wrap around for partly to mostly cloudy conditions for much of Thursday. With the diurnal heating and continuing cyclonic flow aloft, there may be a few isolated to sctrd showers embedded in the CU fields. clear out and sfc wind decrease making for a cool night into Friday morning with widespread lows well down in the 50s.

LONG TERM /FRIDAY THROUGH WEDNESDAY/

Issued at 225 PM CDT Wed Jun 17 2026

Quick look at the longer range suggests some return flow warming for Friday ahead of a clipper-like system that will look to drop down in northwesterly steering flow acrs the western GRT LKS. This will bring a chance for a shower and possible storm in or near the CWA late Friday and Friday evening. Continued warming for Saturday trying to pull some 80s up acrs the local area. Then eyes turn to MCS generation acrs the central plains Sat night, and the potential for this feature to propagate eastward and impact the local area on Sunday sometime with strong storms and heavy rainfall. Beyond that, upper jet ensembles suggests a return to northwesterly steering flow acrs the upper MS RVR Valley early to mid next week making the area susceptible to clipper-type wave generated precip events every other day or so, depending on moisture return for these waves to utilize.

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 616 PM CDT Wed Jun 17 2026

Post frontal winds gusting up to 35 knots will be seen through 03z/18 with a very slow spin down on the gusts through 12z/18. RAP soundings suggest a marginal LLWS risk through 12z/18 in the 1.5-2.0 kft AGL layer. After 14z/18 winds will again jump after the inversion breaks in the morning with gusts reaching 20-25 knots.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Flood Watch until 7 PM CDT this evening for IAZ063>068-076>078- 087>089-098-099. IL...Flood Watch until 7 PM CDT this evening for ILZ009-015>018- 024>026-034-035. MO...Flood Watch until 7 PM CDT this evening for MOZ009-010.